The invention relates to a photo-curing device or appliance suitable for activating photo-curable matrices contained in materials for filling, reconstitution, impression-taking, adhesive bonding, or whitening, in particular for application in the field of dentistry, the device or appliance having a light source and optical and electronic means for controlling, modulating, aiming, selecting, and conveying light energy to a zone that is to be illuminated.
The photo-curing of a material consists in a chemical reaction, e.g. taking place during polymerization, that serves to bond together permanently the macromolecules that make up the material. It is induced by delivering light radiation that enables photo-initiators contained in the material to produce covalent bonds that modify the structure of the material, thus making it possible to obtain the looked-for physical properties, such as hardening of the material or adhesive bonding of the material on a support.
The effectiveness of photo-curing depends firstly on the photo-initiator and on its suitability for creating macroradicals, e.g. on polymer chains, so it must be possible to irradiate the material with wavelengths lying in the photosensitivity spectrum of the photo-initiator present in the material. However, the photo-curable materials that are used for example in the field of dentistry are progressing continuously, as are the photo-initiators included in their compositions, thereby leading to a greater diversity of sensitivity spectra that need to be taken into consideration.
In order to satisfy the needs of practitioners, photo-curing devices therefore need to generate a broad light spectrum suitable for photo-curing materials containing a variety of photo-initiators, such as camphoroquinone (CQ), phenylpropanedione (PPD), and lucirin, for which the target wavelength ranges corresponding to the sensitivity spectra are as shown in FIG. 1.
Furthermore, in most of the materials used, this chemical reaction is an exothermic reaction that causes a rise in temperature of the exposed zones, which temperature rise is made even greater since it is in addition to the temperature rise caused by light energy being absorbed by the tissues themselves.
Present devices, such as those available for dentistry, make use of two types of light source, namely:                either a light source that emits light radiation spread over a broad spectrum, thereby satisfying the broad spectrum problem;        or else a light source that produces radiation over a spectrum that is very narrow, or indeed monochromatic, thus limiting the amount of energy that is delivered, and thereby keeping the heating of the exposed tissues under control.        
For the first category light source, the source used mainly involves halogen bulbs, arc lamps (e.g. xenon lamps), or discharge lamps.
That type of light source produces light radiation over a very broad spectrum. Nevertheless, in terms of the radiation that is useful for interacting with the photo-curable materials used, the efficiency of such sources is quite low even though their purchase price and maintenance remain expensive. Furthermore, that type of light source requires a large amount of energy for its operation associated with an active cooling device (forced convection) for dissipating the heat given off. Consequently, it is difficult to make portable devices that are powered by optionally rechargeable batteries and that use light sources of those types.
Furthermore, a non-negligible fraction of the radiation emitted by those broad spectrum sources lies in the infrared range and that can give rise to unwanted thermal effects on the tissue being treated (e.g. necroses), which effects are in addition to those of the exothermic reaction induced by the photo-curing.
Finally, a complex optical filter system needs to be implemented in order to limit the radiometric power emitted so as to avoid burning the tissue being treated by exposure to infrared radiation.
The second category includes devices making use of light-emitting diodes (LEDs). This type of light source presents the advantage of delivering a spectrum of high efficiency (providing it corresponds to the photo-curable material for treatment), since all of the energy produced is useful for the chemical reaction that is to be initiated. Devices using such sources also present low energy consumption and are consequently suitable for being powered by a self-contained power supply constituted by optionally rechargeable batteries. Their small volume enables a compact ergonomic device to be obtained. Finally, the optical devices used with this type of light source may be considerably simplified since LEDs are generally encapsulated in transparent materials presenting optimum transmission. Such materials are also molded to have a shape that enables integrated optical devices to be made that are suitable for collecting and directing the light energy produced.
Because of the narrow wavelength range covered by the emission spectrum of an LED (of the order of 20 nanometers (nm) for radiation power ≧50%), appliances fitted with only one diode cannot deliver an emission spectrum that is broad enough to initiate photo-curing of a variety of different materials.
In an attempt to remedy that drawback, an existing solution consists in increasing the energy power delivered to the LED beyond a conventional nominal value. That increases the intensity of the radiation emitted by the diode at the margins of its emission spectrum, thereby broadening its working emission spectrum. Nevertheless, under such circumstances, the overall intensity of the radiation is increased, thereby giving rise to temperature rise phenomena in tissues that patients find difficult to accept.
Furthermore, the practitioner does not always know which photo-initiators are contained in the materials being used. Thus even if a practitioner were to have a multiplicity of appliances fitted with LEDs having different emission spectra, the practitioner would still not know which one to use.